1. Field
This disclosure relates generally to an electronically programmable fuse (eFuse), and more specifically, to an improved eFuse structure and method of making the same.
2. Related Art
Electrically programmable fuses (eFuses) generally include a silicide overlying a polysilicon layer, further having a first contact positioned on one end of the silicide and a second contact disposed at a distance from the first contact on an opposite end of the silicide. One contact functions as the anode while the other contact functions as a cathode.
Programming of an eFuse is typically accomplished by forcing a large electrical current through the eFuse. This high current is intended to break the eFuse structure which results in an electrical open. In other words, during programming, it is desirable for the silicide to migrate from the cathode to the anode and thus create an electrical “open” in the silicide.
Furthermore, for conventional eFuse programming, the eFuse structure to be programmed is typically selected by a decoded address which is generated by a control circuit that is powered by a low voltage supply (VDD). An eFuse programming command is created by additional logic circuitry which generates a program enable signal. The program enable signal is converted from the voltage level of the logic supply (VDD) to the voltage level of the programming supply (PVDD) by a level shifter. The program enable signal may be amplified by several driver stages. If an eFuse is selected by the control logic and a program enable signal is present, a current can pass through the selected eFuse for programming.
As such, eFuses have been implemented in integrated circuits as attractive passive devices to electrically repair failures within an integrated circuit product. However, if during programming of the eFuse, the silicide in the eFuse is not completely migrated to its anode from its cathode, then the eFuse is rendered non-functional.
In addition, as poly gates are scaled down to smaller and smaller dimensions, the actual poly media portion in an eFuse becomes smaller and smaller, causing silicide migration through the poly medium to become more and more difficult. In other words, as the gate poly height in an eFuse structure is scaled down, there is concern about full silicidation (FUSI), whereby full silicidation causes a malfunction of the eFuse. Furthermore, it is difficult to produce silicide migration when the medium (e.g., poly) is smaller than a critical dimension.
Accordingly, there is a need for an improved method and apparatus for overcoming the problems in the art as discussed above.